Luminous signs employing a gaseous discharge and the methods for making these signs have been disclosed in several patents. In general, these signs are made by using two or three glass plates where in one or two of the plates is formed a groove or cavity corresponding to the desired display. The cavity is hermetically sealed and attached to a gas entry port incorporating a set of electrodes. In the manufacturing process the cavity is evacuated and a quantity of gas, such as neon, is introduced into the cavity through the gas entry port. The gas is then ionized by applying a voltage across the electrode set. The ionized gas, in turn, causes the display to illuminate.
Heretofore, the electrodes typically consisted of a metal cylinder open on one end and enclosed in a glass tube and having a metal wire which passes through the glass tube to contact the metal cylinder. The electrodes must be prepared prior to use by heating the electrodes to a high temperature under vacuum sufficient to form a metal rich oxide film over the electrodes. The oxide film is of a type commonly associated with thermoionic cathodes, for example, primarily barium oxide. It will be appreciate that heating the electrodes decomposes the metal carbonates to form a metal rich oxide surface which is the electrode surface. The electrodes are typically heated by applying an electric current between the electrodes. It will be appreciated that the metal oxide electrode surface requires formation at temperatures approaching 900 degrees celsius. A gas discharge of a high current sufficient to cause heating of the electrodes to the necessary temperature is ignited typically using air. This approach is described in U.S. patent application Ser. No. 08/658,352, entitled "Luminous Gas Discharge Display", incorporated herein by reference.
Removing the contaminants from the sign improves the life of the sign. The contaminants which are removed during the formation of the electrode are best removed by heating the entire flat sign or tube. However, it will be appreciated that the process of forming the electrodes can also cause strong heating of the channel or tube and also cause breakage in the case of flat panel signs.
Although the many known variations of electrodes for luminous signs have been proven to perform satisfactorily, further improvements of electrodes for luminous signs and methods of manufacture are desired.
Accordingly, it is an object of the present invention to provide a low profile electrode assembly for a luminous gas discharge display and a method of manufacturing the electrode assembly that overcomes problems of the prior art. For example, it is an object of the present invention to provide a method of manufacturing a low profile electrode assembly for a luminous gas discharge display that does not require intense heating of the electrode to form the electrode. Yet another object of the present invention is to provide a low profile electrode assembly which is mounted on the rear of a luminous gas discharge display external of the display. Another object of the present invention is to provide an electrode assembly which produces a spray discharge in a suitable ionizable gas. Still another object of the present invention is to provide a durable electrode assembly which is immune to typical vacuum contaminants and provides a long life performance. Another object of the present invention is to provide a method of manufacturing electrodes of a luminous gas discharge display that is simple and economical.